The present invention relates to a voltage regulator for a vehicle mounted generator having a rectifier and, particularly, to such regulator for regulating an output voltage of the rectifier of the generator.
FIG. 1 is a circuit diagram of a conventional voltage regulation system for a vehicle mounted generator in which a generator 1 is composed of an armature winding 101 and a field winding 102. A rectifier 2 includes a main rectifier portion having an output terminal 201 for providing a main d.c. voltage obtained by a fullwave rectification of an output a.c. voltage of the generator 1 and an auxiliary rectifier portion having an output terminal 202 for energizing the field winding 102 as well as detecting an output voltage of the generator 1. The rectifier 2 further includes an output terminal 203 which is grounded. The voltage regulator 3 includes a series connected resistors 301 and 302 which form a voltage divider for dividing a voltage at a positive terminals of a battery 4 and responds to a fraction of the battery voltage to regulate the output voltage of the main rectifier portion of the rectifier 2 and hence the output voltage of the generator 1 to a predetermined value. The regulator 3 further includes series connected resistors 303 and 304 which form a second voltage divider for dividing the voltage at the output terminal 202 of the rectifier 2 to detect the output voltage of the generator 1, similarly.
An input transistor 308 of the regulator 3 has a base connected through a reverse current blocking diode 305 and a Zener diode 307 to a dividing point of the voltage divider 301, 302 and through the Zener diode 307 and a reverse current blocking diode 306 to a dividing point of the voltage divider 303, 304. The Zener diode 307 detects the voltage at the dividing point of either of the voltage dividers and turns on when the voltage exceeds a pre-set value. The input transistor 308 is turned on when the Zener diode 307 is turned on.
The regulator 3 further includes an output transistor 309 having a base connected to a collector of the input transistor 308 and through a resistor 310 to the output terminal 202 of the rectifier 2, a collector connected to one of terminal of the field winding 102 and through a reverse current blocking diode 311 to the terminal 202 of the rectifier 2, and an emitter connected to an emitter of the input transistor 308 which is grounded.
The output transistor 309 is turned on and off under control of the input transistors 308 to on-off control the field winding 102. The transistors 308 and 309 and the Zener diode 307 constitute switching means for the on-off control of the field current according to the voltages detected by the voltage dividers. The reverse current blocking diode 311 serves to absorb on-off surges produced in the field winding 102.
A load 5 is connected to the positive terminal of the battery 4, which is connected to the output terminal 201 of the rectifier 2, and through a key switch 6, a resistor 7 and a reverse current blocking diode 8 to the output terminal 202 of the rectifier 2 for the initial energization of the field winding 102.
In operation, when the key switch 6 is closed to start the vehicle engine, an initial energizing current flows from the battery 4 through the key switch 6, the resistor 7 and the diode 8 to the field winding 102 to make the generator 1 ready for operation.
Then, when the engine starts, the generator 1 commences its operation to supply an a.c. output which is rectified by the rectifier 2 and supplied to the battery 4 to charge the latter and to the electric load 5.
The voltage regulator 3 responds to the voltage at terminal S of the battery 4 to regulate the voltage to a predetermined value. That is, when the terminal voltage exceeds the predetermined voltage which is detected by the voltage divider composed of the resistors 301 and 302 and the Zener diode 307, the diode 307 is turned on to thereby turn the input transistor 308 on which, in turn, turns the output transistor 309 off. Upon the cut-off of the latter transistor, field current no longer flows through the field winding 102, resulting in no output power generated by the generator 1.
When the generator 1 stops its power generation, the voltage at terminal S of the battery 4 is gradually lowered and therefore the voltage at the junction of the resistors 301 and 302 is also lowered gradually.
When the output voltage of the voltage divider is lowered below the preset value, the Zener diode 307 is turned off to turn the output transistor 309 on and to connect the field winding 102 in circuit, resulting in an increase of the output voltage of the generator 1. The terminal voltage of the battery 4 is regulated at a constant value by repetition of the above mentioned operations.
When the connection of the regulator 3 to terminal S of the battery 4 is broken due to incorrect mountings or abnormal shock or vibration of the vehicle, however, the voltage across the voltage divider composed of the resistors 301 and 302 becomes zero and thus the transistor 309 continues to conduct. Therefore, the generator 1 tends to run without control of the regulator, while the voltage divider composed of the resistors 303 and 304 is still applied with the output voltage at the output terminal 202 of the rectifier 2. When the output voltage at the terminal 202 exceeds a second preset value which is determined by the resistors 303 and 304 and the Zener diode 307, the latter diode is turned on and, when the voltage is lowered below the second preset value, the diode 307 is turned off. The operations are repeated so that the output voltage of the generator 1 is regulated to a constant value even when the voltage regulator 3 is disconnected from the detection terminal S.
As mentioned above, when the connection of the voltage regulator 3 to the detection terminals is broken, the voltage detection criteria is switched from that for the battery voltage to that for the output voltage of the rectifier 2 of the generator 1, and the voltage dividers and the Zener diode thus constitute a protection circuit against the case of breakage of the connection of the regulator to the detection terminal S.
The first preset value and the second preset value are preferably selected identical or at least substantially equal to each other to prevent the overcharging of the battery and to accommodate the durations of various electric loads of the vehicle.
However, when the electric load of the vehicle is increased, the output current of the generator 1 increases correspondingly, resulting in an increased voltage drop along the main wiring 9 and in a higher output terminal voltage of the generator than the terminal voltage of the battery.
Peaks of a ripple contained in the output voltage of the generator may be absorbed by the so-called capacitance effect on the battery side. However, on the generator side, the ripple which contains relatively high peaks is supplied from the output terminal 202 of the rectifier 2 to the voltage divider composed of the resistors 303 and 304.
For these reasons, when the values of the first and second preset voltages are not selected the same or substantially the same, the regulator operates in accordance with the highest one of them. Therefore, during a normal operation of the generator having a heavy load, the regulator always operates on the basis of the output voltage of the rectifier, which makes the regulation of the battery charging voltage to a constant value impossible. Consequently, in the conventional system, the second preset value is usually set at a value higher by about 1.5 volts to about 2.0 volts than the first preset value which is the battery detection voltage, in order to keep the battery charging voltage constant regardless of the load condition of the generator during normal operation.
In a system having the first and second preset values selected as above, when the regulator is disconnected from the detection terminal S of the battery, the latter and other electric loads of the vehicle are applied with the second preset voltage which is higher than the battery detection voltage. Therefore, the battery tends to be overcharged, resulting in a shortened life thereof, and the power consumption of the other electric loads increases.
U.S. Pat. No. 3,942,097 discloses a voltage regulating system in which a single voltage divider is used for detecting both the battery voltage and the rectifier output voltage. In this system, the voltage divider comprises a pair of resistors connected in series through a Zener diode having a cathode connected through a resistor to a collector of an input transistor whose base is connected through a resistor to a detection terminal of a battery. The collector of the input transistor is connected to a base of a transistor having a collector-emitter circuit connected to an alarm lamp. When a connection of the base of the input transistor to the battery through the base resistor is broken, the lamp is lit by a current flowing through the collector-emitter circuit of the transistor to indicate the disconnection.
The rectifier output voltage is applied to the divider through a couple of series connected diodes which act as a compensating circuit for making a voltage to be applied from the rectifier across the divider as close to that to be applied from the battery as possible. That is, the compensating circuit has to be employed due to the fact that the rectifier output voltage becomes much higher than the battery voltage.
However, it is very difficult practically to select a composite resistance value of the plurlaity of series connected diodes exactly and this system is relatively expensive in construction and manufacture. Further, since the single voltage divider is supplied with the rectifier output voltage and the battery voltage, there is a mutual interference therebetween even if such compensating circuit is provided.